This invention relates to a drum-type sand classifier which has a cone-shaped discharge chute that effectively discharges the classified sand and is employed instead of the conventional belt conveyor.
Generally speaking, there are several methods of separating solid particles into groups which have the same particulate size range. An effective method is screening which is performed by making use of the difference of the size of particles to be classified but not of the difference of the specific gravity of the particles. However, when the classification of minute particles which have a diameter of less than 0.1 mm is required, this screening method is no longer useful.
Another effective method of separating particles into groups of the same particulate size range is called "classifying". Classifying makes use of the settling velocity of solid particles which are in a fluid body and the above velocity varies corresponding to the size as well as the specific gravity of the solid particles. This classifying generally consists of "wet classifying" which uses water as the fluid body and "dry classifying" which uses air as the fluid body. Since the viscosity coefficient of water is 50 times greater than that of air, the settling speed of solid particles also varies greatly depending on the fluid body used. Accordingly the size of a solid particle that can be classified is around 10.mu. - lmm with "wet classifying" while it is around 1.mu.-lmm with "dry classifying".
The sand classifier of this invention makes use of the wet classifying method by which even the muddy component can be eliminated (classified) from muddy water which results in the production of clear water.
The wet-type clasifiers generally comprise rake-type, spiral-type and drum-type classifiers. The first two of the foregoing types of classifiers, however, are seldom used any longer since their classifying efficiency is low and they cannot keep up with the demand for sand which is remarkably increasing these days. Therefore, the drum-type classifier is predominantly used.
The apparatus of this invention which is hereinafter disclosed is also a drum-type classifier, however, it differs greatly from the conventional classifier. The conventional one requires a belt conveyor which is inserted into the rotary drum of the classifier and discharges the classified sand out of the drum and is an indispensable element of apparatus, while the classifier of this invention has a unique discharge means which is integral with the rotary drum. The discharge system of the invention which is completely new and basically different from the conventional system is due to the above discharge means which results in a remarkable improvement of the classification efficiency, a great increase in the amount of sand that is discharged without sacrificing the compactness of the apparatus and a drastic decrease of mechanical failures which are caused due to friction or corrosion of the parts of the apparatus.
Since the conventional drum-type classifier requires a belt conveyor which is placed into the drum from the outlet, the outlet, which is located at the rear of the drum, must be large enough for the loading of the conveyor, which results in a low capacity for classification since the volume of muddy water which can enter the drum is small as is the amount of classified sand which is discharged from the drum.
Here, two drums are compared in order to understand the relationship between the capacity of the drum and the diameter of the outlet which is located at the rear end of the drum. Both drums have an equal length of 3.0m and an equal diameter of 2.5m. One drum has an outlet diameter of 1.7m while the other has an outlet diameter of 1.0m. Due to this structural difference, the volume of muddy water which can be retained in the latter drum is 2.3 times greater than that of the former drum since the outlet diameter is smaller. This implies that if the aforementioned belt conveyor is no longer required, a compact classifier which does not sacrifice the volume of sand discharged from classifier can be constructed.
It is an object of this invention to provide a drum-type classifier which has a cone-shaped discharge means that is formed as an integral part of the classifier and is employed for discharging the classified sand rather than using the conventional belt conveyor. Since the discharge means is an intergral part of the rotary drum, the classified sand is smoothly discharged from the drum while the drum rotates.
In the case of the conventional classifier where the rotary drum and the discharging means are independently operated, parts of the apparatus are always subject to severe frictional wear caused by sand, giving rise to various mechanical failures or accidents, which are difficult problems and remain unsolved.
It is another object of this invention to provide a classifier which produces classified sand with improved uniformity of classification set within certain limits as compared to the sand that is classified by the conventional classifiers. Due to the lowering of the percentage of mud which remains in the classified sand, sand with few mud components can be obtained which can be used to produce cements which have high rigidity.
It is still another object of this invention to provide a classifier which is capable of separating the mud from the larger sand components and is further capable of classifying the mud into coarse mud which remains in the water and discharged with it through the water discharging outlet.
The construction and operation of this invention, however, together with additional objects and advantages thereof, will be best understood from the following description of the specific embodiments when read in conjunction with the accompanying drawings.